Well... you asked for it  :P  I've gotten somewhat wild and crazy with some of these but it's everything I could think of.

CaveWorks Wish List
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Walls and such of course (altough it would be great if the system allows for building large cave "rooms" so we'd be able to have a home for dragons and such... many systems I've seen don't let you build larger cave "rooms" well)
Stalagmites (I always get that one and Stalagtites confused)
Limestone columns
Campfires
Bedding (could just be a flat floor tile for a pile of furs/straw and such)
Boulders (I have no idea how to make these other than print a page and crumple it up which actually could work in some situations)
Scree (I think that's the term for it... small rocks and gravel in a pile often adjacent to a wall or cave in)
Crystal formations
Ore veins (preferably multiple colors to represent different types of ore)
Chasms (probably tiles)
Underground rivers (also tiles I'm guessing)
Lava flows (tiles again probably)
Lastly... perhaps instructions for using real-world materials to enhance the cavern... a small bit of gravel makes great boulders/scree and anybody can get a handful of gravel.


CastleWorks Expansion (or CW2)
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Round Towers (preferably multiple sizes or some method of altering size so we can do tall thin towers or squat fat towers or some combo thereof)
Octagonal Towers (again multi size)
Tower Caps (Conical/Pyramidal depending on tower shape... possibly with different colors available or maybe even one that's "glass")
Tower addons (those little sub-towers that are sometimes found near the top of a tower or tower flares where the tower flares out at the top to be somewhat wider)
Alternate wall textures (I know this one is a big one because you'd need to do alternate textures for the existing CW pieces then)
A drawbridge (actually kinda surprised this one isn't in the first CW)
Curved walls (could do this with CW as is but don't have the wall tops for the soldiers/archers to stand on)
Non-Right Angle Walls (walls that meet at a 30 degree angle or maybe at a 120 degree angle for non-rectangular castles... can probably be done with CW as is by just cutting the wall segments shorter on one side than the other but real instructions/suggestions would be great)
Outbuildings (Stables, barracks, that kind of thing)
Props (Catapults, Ballista, archery targets, training dummies, maybe even flags?)

The biggest problem I see with a "one size fits all" CastleWorks system is the main building... they're almost always unique to the castle.  Deal Castle doesn't have one per se, Caernarfon sorta does and doesn't, and Neuschwanstein has it kinda built into the walls and towers.

And for a final thought... I'd be thinking ahead on this kind of thing for say VillageWorks by making buildings somewhat modular if possible.  Say what if that style of building where the bottom floor was smaller than the floors above it (to avoid taxes actually) was set up so we could use the bottom from one building with the top of another or something like that.  Or choose an alternate roof.  The big plus is that this would let us make many many more buildings that are unique by selecting the parts to use in constructing it.  Obviously this doesn't work for some buildings (like the absolutely stunning smithy you've got in CastleWorks) but where possible it would be cool.

All incredible ideas Adam! I will be sure to include them in some shape or form in future sets! Thank you for the wonderful variety of suggestions!